In a typical pneumatic transfer system, an article carrier is propelled by air pressure between two spaced-apart terminals through an elongated transfer tube. The carrier is propelled through the transfer tube-by creating a pressure differential across the carrier, the carrier being propelled forward by a higher air pressure behind a carrier than exists in front of it. The pressure differential may be created by a blower system forcing air into the transfer tube behind a carrier (thereby creating increased pressure behind the carrier) or by creating a vacuum in front of the carrier (thereby reducing pressure ahead of the carrier).
A carrier is generally cylindrical in shape and typically includes spaced-apart wear rings, conventionally referred to as "accelerator rings", which surround the carrier and generally seal the carrier against the inner surface of the transfer tube. The accelerator rings engage the inner surface of the transfer tube and typically support the weight of carrier as it travels through the tube. An accelerator ring may be made from a wide variety of materials. The type of material used for an accelerator ring is generally based upon the size of the carrier and the weight to be carried thereby. In this respect, soft resilient materials, such as felt or belting, may be used for small diameter carriers transferring relatively small loads. For large weight-carrying carriers, hard rubber or rubber reinforced leather belting is normally used.
In the past, most transfer tubes were constructed from commercially available, standard, metal tubes. In recent years, however, it has been known to form transfer tubes from plastic tubing because of its light weight, and the relative ease of installing such material. Polyvinyl chloride (PVC) tubing has found particular acceptance in pneumatic tube systems because of its commercial availability and its relatively low cost.
A problem with the use of PVC tubing, however, is that it is apparently not compatible with accelerator rings known heretofore. Specifically, a powdered residue is produced within the terminals of pneumatic transfer systems utilizing PVC tubing. In addition, noticeable wear of the accelerator ring is produced on carriers used in such systems. It is believed that these problems are caused by the PVC being abraded by the accelerator ring, and further by friction generated between the accelerator rings and the inner surface of the PVC tubing which creates sufficient heat to breakdown the inner surface of the PVC tubing. In this respect, it was noted that conventional accelerator rings, which are typically formed of rubber-impregnated belting or a NYLON synthetic Velcro.RTM. strip, causes the inner surface of PVC tubing to breakdown. In this respect, solid PVC is relatively soft material having a combination of amorphous and crystalline regions. It is believed that heat generated between the accelerator ring and the surface of the tubing, as well as the abrasive effects of the harder belting or nylon, causes the amorphous regions of the PVC tubing to break down, thereby causing thin layers or particles of the PVC to peal away from the inner surface of the tubing. These layers or particles breakdown into dust and particulate as they are driven by the accelerator rings (and by the differential pressure) through the transfer tube. The dust or powder eventually collects and settles within the terminals and on the carrier itself. As will be appreciated, this is particularly undesirable in pneumatic tube systems used by the general public, such as in pneumatic systems used by financial institutions.
Accelerator rings made of felt do not exhibit the problems set forth above when used in PVC tubing, and therefor are suitable for use in small-load carrying pneumatic tube system. The production of felt, however, produces undesirable and hazardous by-product, and it is believed that in the near future the production of such material may be banned or restricted. It is therefore desirous to develop a non-felt accelerator ring which does not abrade or break down plastic tubing.
The present invention overcomes these and other problems and provides an accelerator ring for a carrier used in a pneumatic tube system, which accelerator ring reduces the wear and friction created between the ring and the surface of a pneumatic tube system by utilizing a soft, non-abrasive material having a relatively low coefficient of friction.